Interstitial water phase

In sediments, the immobilization of heavy metals often occurs by sulfide formation. Pollutants can become remobilized by sediment oxidation after lowering of the water table or by erosion (Forstner 1995). The solution composition of the interstitial water phase is the most sensitive indicator of pollutant reactions with surfaces (Forstner et al. 1999). A comprehensive description of the reactions of inorganics in anoxic sediments was provided by Song and Muller (1999). 

As is the case with assessments of the toxicity of dissolved trace metals, the development of sediment quality criteria (SQC) must be based on the fraction of sediment-associated metal that is bioavailable. Bulk sediments consist of a variety of phases including sediment solids in the silt and clay size fractions, and sediment pore water. Swartz et al. (1985) demonstrated that the bioavailable fraction of cadmium in sediments is correlated with interstitial water cadmium concentrations. More recent work (e.g., Di Toro et al, 1990 Allen et al., 1993 Hansen et al, 1996 Ankley et ai, 1996, and references therein) has demonstrated that the interstitial water concentrations of a suite of trace metals is regulated by an extractable fraction of iron sulfides. 

Polychaete worms belonging to the genera Nereis and Scolecolepides have extensive metabolic potential. Nereis virens is able to metabolize PCBs (McElroy and Means 1988) and a nnmber of PAHs (McElroy 1990), while N. diversicolor and Scolecolepides viridis are able to metabolize benzo[a]pyrene (Driscoll and McElroy 1996). It is worth noting that apart from excretion of the toxicant, polar, and mnch more water-soluble metabolites such as the glycosides formed from pyrene by Porcellio sp. (Larsen et al. 1998) may be mobile in the interstitial water of the sediment phase. 

Brannon and Patrick [129] reported on the transformation and fixation of arsenic V in anaerobic sediment, the long term release of natural and added arsenic, and sediment properties which affected the mobilization of arsenic V, arsenic III and organic arsenic. Arsenic in sediments was determined by extraction with various solvents according to conventional methods. Added arsenic was associated with iron and aluminium compounds. Addition of arsenic V prior to anaerobic incubation resulted in accumulation of arsenic III and organic arsenic in the interstitial water and the exchangeable phases of the anaerobic sediments. Mobilization of... 

The water is transported from the intraparticle phase to the interstitial gas phase. It is then further transported through the porous system of the bed towards the bed surface by means of forced convection. 

Similar to Sites 994 and 995, six indicators of hydrate were present (1) large gas exsolution from cores, (2) high methane sediment concentration, (3) BSRs, (4) low interstitial-water chlorinity, (5) low core temperatures (although IR technology was introduced just after this hydrate leg), and (6) P-wave velocity logs and resistivity logs. As in Sites 994 and 995, there was a discrepancy between the indicated base of the inferred hydrate zone (452 mbsf) and the phase-equilibria stability zone (491 to 524 mbsf). 

Ozretich, R. J., L. M. Smith, F. A. Roberts. 1995. Reverse phase separation of estuarine interstitial water fractions and the consequences of C1S retention of organic matter. Environmental Toxicology and Chemistry 14 1261. 

Wet sediment phase Solid phase obtained after extracting pore (or interstitial) water from whole sediment. Porewater is commonly extracted by centrifugation (e.g., at 3,000 rpm, 30 min, 15°C). Volume 2(8). 

Most sediment toxicity tests have been conducted in the laboratory with single species of freshwater and marine benthic organisms such as amphipods and midges, but in some cases planktonic species also have been used. Most tests conducted to date have been acute and have been of 10 days duration or less. Sediment toxicity tests are conducted with the solid phase or the pore water (interstitial water). Methods have been published describing the collection and preparation techniques. 

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